Hodoscope readout system

ABSTRACT

A readout system has been provided for reading out a radiation multidetector device with a reduced number of signal sensors. A radiation hodoscope, such as an array of scintillation counters, multiwire proportional counter array, or a set of multidetectors which do not receive signals simultaneously, is divided into equal numbered groups. A first group of signal terminals is connected to the equal numbered groups of detectors so that a signal from any one of the detectors of a group will be fed to an individual one of the first group of terminals. A second group of signal terminals is connected to the detector groups so that a signal from a particular numbered detector of each of the detector groups is connected to individual ones of the second group of terminals. Both groups of signal terminals are, in turn, coupled to signal sensors so that when a signal is simultaneously observed in one of the first group of terminals and one of the second group of terminals the specific detector detecting a radiation event is determined. The sensors are arranged in such a manner that a binary code is developed from their outputs which can be stored in a digital storage means according to the location of the event in the multidetector device.

United States Patent 1 Lee [ 1 Dec.4, 1973 HODOSCOPE READOUT SYSTEM [75]Inventor: Lap Yen Lee, Houston, Tex.

[73] Assignee: The United States of America as represented by the UnitedStates Atomic Energy Commission, 7 Washington, DC.

[22] Filed: Nov. 8, 1972 [21] Appl. No.: 304,863

Primary Examiner-Harold A. Dixon Attorney-John A. Horan [57] ABSTRACT Areadout system has been provided for reading out a DISC iQNS DISCDIGITAL STORAGE radiation multidetector device with a reduced number ofsignal sensors. A radiation hodoscope, such as an array of scintillationcounters, multiwire proportional counter array, or a set ofmultidetectors which do not receive signals simultaneously, is dividedinto equal numbered groups. A first group of signal terminals isconnected to the equal numbered groups of detectors so that a signalfrom any one of the detectors of a group will be fed to an individualone of the first group of terminals. A second group of signal terminalsis connected to the detector groups so that a signal from a particularnumbered detector of each of the detector groups is connected toindividual ones of the second group of terminals. Both groups of signalterminals are, in turn, coupled to signal sensors so that when a signalis simultaneously observed in one of the first group of terminals andone of the second group of terminals the specific detector detecting aradiation event is determined. The sensors are arranged in such a mannerthat a binary code is developed from their outputs which can be storedin a digital storage means according to the location of the event in themultidetector device.

11 Claims, 7 Drawing Figures PATENTEUHEE 41m SHEET 1 BF 6 m5 umE :ooov

(D U) U) U) U) U) U) (D U) l l l (D G) \l 03 U h OI N X- COORDINATE Y-COORDINATE STOP PATENTED DEC 41973 sum u 0F 6 PAIENIEDBEB 41918 3,777.161

' sum 5 or 6 FIELD OF VIEW PM 2 FIELD OF 63 VIEW PMI GI/EI FIELD OF VIEWFIELD OF VIEW PM 2 FIELD OF VIEW PM 1 FIELD OF VIEW HODOSCOPE READOUTSYSTEM REFERENCES U. S. Pat. No. 3,308,438, issued Mar.' 7, 1967, toPhilip Spergel et al. for An Au'tofluoroscope."

Holdoscope Design To Minimize Photomultiplier Use," by L. W. Alvarez,Review of Scientific Instruments, Vol. 31, No. l, 1960, p. 76.

U. S. Pat. No. 2,632,058, issued Mar. 17, 1953, to Frank Gray for APulse Code Communicator.

Mathematical Games, by Martin Gardner, Scientific American, August 1972,pp. 106-109.

BACKGROUND OF THE INVENTION The present invention was made during thecourse of, or under, a contract with the United States Atomic EmergyCommission.

This invention relates generallyto radiation multidetector readoutsystems and more specifically to a multidetector readout system fordigital processing with a minimum of interfacing equipment.

In radiation multidetector devices, especially for spatial radiationdetection, it is common practice to monitor spatial'radiation detectionsystems, such asmultiwire proportional counters or arrays ofmultidetectors, by separate detection channels for each element of amultiwire counter, multielement scintillation counter or othermultidetector arrays. Individual events in dis- .crete portions of adetector array are sensed individually by separate detection channelsand fed into a memory device by means of an X-Y coordinate addressregister. This straightforward technique requires a number of detectionchannels at least equal to the number of increments of resolution alongthe X and Y axis of the detector array or multiple wire array. Thesedetector systems may be composed of hundreds or-even thousands ofradiation detection'elements in a spatial detection system, therebyrequiring hundreds of signal sensing channels for readout and recording.I

A typical system of the prior art is described in the above-referencedU.S. Pat.'No. 3,308,438.

The apparent prior necessity for a number of detection'channels equal toat least the number of X and Y resolution components of a detector arrayto locate an eventfor storage becomes expensive and'difficult toconstruct for detector system arrays with hundreds of resolutioncomponents or collector wires. Thus, there is a need for a system forreading out a radiation multidetector device without the complexity andexpense of prior readout devices and providing the readout in digitalform.

Radiation detection devices have been provided in the art of radiationdetection which provide a digital coded output. These devices employmasks which block portions of the detector in a mannerto'provide thedigital readout. This technique has been used primarily to determine theposition of a beam ofv radiation along the length of a plurality ofdetectors. The beam of radiation is directed onto the detectorstransversely to its length and as it is moved along the detectors. Themasking means through which the radiation impinges on the detectorsalong parts of their length produces at the various outputs from thedifferent detectors a digital indication of the position of the beamalong the detectors.

A similar technique has been developed by L. W. Alvarez for a spatialdetection system in which layers of scintillation material aredifferently masked and each optically coupled to separatephotomultiplier tubes from which a binary coded signal is developed toindicate the position of radiation through the detector layers. Thisdesign requires that the number of photomultiplier tubes be equal to thenumber of layers of the detector, e.g., five layers are required for a64-element linear array and ten layers for a 64 X 64 element array. Thepresent invention requires only a single layer for a linear array and,in one embodiment, two layers for an X-Y hodoscope regardless of thenumber of detectors or the number of photomultiplier tubes. Therefore,in the present invention the thickness of the'hodoscope can be reducedgreatly'over that proposed by Alvarez, which is often necessary in themeasurement of radiation. This present method can also be utilized forgamma ray mapping, such as in a gamma ray camera, which could not beachieved by a-multilayer design.

SUMMARY OF THE INVENTION In view of the above, it is an object of thisinvention to provide a radiation hodoscope readoutsystem which requiresa minimum number of readout channels for proved method of mapping gammaray images.

Yet another object of this invention is to'provide a one or twodimensional digital readout system from a single layer of scintillationmaterial.

Briefly, this invention is a digital readout system for a spatialradiation detection medium which generates a signal at a locationindicative of the position of a radiation event detected by a radiationsensitive area lying within a single plane in the detection medium,comprising a plurality of signal terminals; a signaltransmitting meansfor connecting selected groupings of the radiation sensitive areas ofthedetectingmedium to respective ones of said signal terminals; a pluralityof signal sensing means responsive to signals from selected groupings ofthe signal terminals for generating a digital coded signal whose code isindicative of the location of the event within the-detection medium; andmeans for recording said digital signal.

Other'objects and many of the attendant advantages of the presentinvention will beobvious from the following detailed description takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of asimple embodiment of a multidetector readout of the present invention.

FIG. 2 is a schematic diagram of a multidetector readout system whichprovides two-dimensional readout.

FIG. 3 is a schematic diagram of an alternate readout system for usewith the detector array of FIG. 2 for twodimensional readout.

FIG. 4 is a schematic diagram of an alternate light pipe connectionscheme according to the present invention for readout of a largearray ofdetector elements.

FIGS. 5 and 6 are diagrams of the geometric arrangements of the lightterminals of FIG. 4 which are viewed by photomultiplier tubes whoseregion of view normal to the plane of the terminals is shown by circles.

FIG. 7 is a schematic diagram of an alternate twodimensional detectorreadout system according to the present invention.

DETAILED DESCRIPTION Referring now to FIG. 1, there is shown an array ofdetecting elements in the form of a plurality of scintillation strips 5.Although only nine strips, indicated as 8-1 through 8-9, are shown toillustrate the invention, it will be understood from the followingdescription that any number of scintillation strips or other radiationdetection means may be read out in the same manner. As illustrated inFIG. 1, it will be seen that only four photomultiplier tubes 7-13 arenecessary to provide a digital readout which will indicate any one ofthe nine scintillation strips detecting a radiation event. Typically,the strips 5 are wrapped, or coated, with the exception of the two endportions with a material, which is opaque to light and yet pervious toionizing radiation, such as aluminum foil to prevent light emittingscintillations in one of the strips from being transmitted throughadjacent strips. The light scintillations generated in the strips 5,caused by absorption of ionizing radiation, are transmitted to thephotomultiplier tubes 7-13 by means of uniform cross section light pipes15, typically fabricated from lengths of Lucite or other suitablelight'conducting material. To derive a digital code in the simplestmanner, the strips 5 are connected to'corresponding ones at thephotomultiplier tubes according to Table I.

TABLE I Binary No. Code Light Pipe Connections (1000) (0100) (0010)(0001) l (0001 S-1 2 (0010) 8-2 3 (001 l 5-3 5-3 4 (0100) 8-4 5 (0101)8-5 5-5 6 (0110) 8-6 5-6 7 (0111) 8-7 8-7 8-7 8 1000) 8-8 9 (1001) 5-98-9 Thus,,it will be seen from Table I that any number of strips may beadded .to the array and connected to photomultiplier tubes to provideabinary coded output which can be stored in a digital storage means 17 orconverted to an analog signal for display on an oscilloscope, forexample, by employing a digital-to-analog converter.

As shown in FIG. 1, the outputs of the photomultiplier tubes 7-13 areconnected to corresponding pulse discriminators 19-25 which convert theapproximately 100 millivolt spike at the output of a photomultipliertube to a 10 nanosecond, 1 volt pulse which can be used to trigger thedigital storage device 17. The storage device 17 may be any type ofwell-known storage devices which have inputs according to bits of abinary code (2 2") which may be connected, respectively, todiscriminators 19-25.

A system made up of n PM tubes thus connected is capable of handling 2"strips. When several similar counters are used in a system where chargedparticles are expected to penetrate two or more counters, PM tube noisecan be eliminated by requiring coincidence between counters. However,when one such counter is used independently, it is necessary to usecodings as 4 shown in Table II where the signal from each event ispicked up by at least two PM tubes.

Referring now to FIG. 2, there is shown an alternate embodiment of areadout system for two-dimensional radiation detection from an array ofscintillator strips 5 identical to those of FIG. 1. In FIG. 2 likereference numerals indicate identical parts to those shown in FIG. 1.The light pipes 15 are shown schematically as single lines to aid insimplifying the drawing and are connected to photomultiplier tubes 7-13according to a prescribed binary code of Table 11.

TABLE II Binary No. Code Light Pipe Connections PM-13 PM-ll PM-9 PM-7(1000) (0100) (0010) (0001) 1 0101 (5) 5-1 8-1 2 O1 10 (6) 5-2 5-2 3 0111 (7) S-3 S-3 S-3 4 1001 (9) 8-4 8-4 5 1010 (10) 8-5 S-5 6 1011 (ll)S-6 S-6 7 1101 (13) 5-7 S-7 S-7 8 1110(14 )S-S 5-8 5-8 9 1111 (15) 5-98-9 5-9 8-9 It will be seen from Table II that a binary code is selectedwhich insures that each strip 5 is connected to at least onephotomultiplier tube on the right end and at least one on the left endfor a purpose which will now be explained.

The photomultipliers 7-13 are again connected to discriminators 19-25,as in FIG. 1, which are, in turn, connected to the inputs of adigital-to-analog converter 31. The converter 31 provides an analogoutput signal whose amplitude is indicative of the one of saidscintillation strips 5 detecting an event. This signal may be used toactivate the X-coordinate input of an X-Y recorder, such as the X-Yoscilloscope 33, shown in FIG. 2. By connecting the photomultipliertubes 7-13 as shown, a timing circuit means may be used to obtain aY-coordinate signal which indicates the position of the event along ascintillator strip 5.

The outputs of discriminators 19 and 21 are connected to the inputs ofan OR gate 32 whose output is connected to the' start input 'of atime-to-amplitude converter (TAC) 35. The outputs of discriminators 23and 25 are connected to-the inputs of another OR gate 37 whose output isconnected through a delay circuit 39 to the stop input of TAC 35. Thedelay 39 is set at a value which is equal to or greater than thepropagation time of a light pulse through the length of a strip 5. Theanalog signal output from TAC 35 is then indicative of the position ofan event along a strip 5.

The Y-coordinate signal from TAC 35 is also connected to theoscilloscope 33, or other X-Y recording device, at the Y-axis inputthereof. The oscilloscope may be synchronized by applying a sync pulseto the Z input thereof. An AND gate 41 is provided which has one inputconnected to the output of OR gate 32 and the other input connected tothe output of delay circuit 39. The output of AND gate 41 is thenconnected to the Z input of oscilloscope 33. A sync pulse is generatedwhen the stop signal is applied to TAC 35 at which time both the X and Ycoordinate signals are present for recording. The output pulses from thediscriminators 19-25 must be set at a width which will insure that ANDgate 41 is activated by the delay stop pulse.

1 In operation, the circuit of FIG. 2 will provide an X-Y recording ofan event within the plane of the multiple scintillation strips 5. Apulse from either photomultiplier tube 7 or 9 will start atime-to-amplitude conversion in TAC 35 which is stopped at a delayedtime after a pulse from either photomultiplier tube 11 or 13. Since allthe light pipes 15 are of equal length, the time measurement is anindication of the position of the event along the strips 5 and providesthe Y-coordinate signal. This signal is combined with'the X-coordinatesignal from D/A 31 and recorded at the end of a TAC 35 conversion toindicate the position of the event on the X-Y oscilloscope 33.

Again it will be understood that any number of strips may be added tothe hodoscope array as long as the binary coded signal provides at leastone signal from each end of the array of strips 5. A very convenientcoding for a large number of arrays will be discussed laterin thisapplication.

Referring now to F IG. 3, there is shown another circuit means forobtaining a two-dimensional (X-Y) output from an array of scintillationstrips 5, as shown in FIG. 2. Beginning with the photomultiplier tubes7-13, which are connected by means of light pipes 15 to the right andleft ends of nine strips 5, as shown in FIG. 2, the sync pulse (Z) isobtainedin the same manner as by connecting the outputs, ofdiscriminators 19 and 21 to the inputs of OR gate 32 and the outputs ofdiscriminators 23 and 25 to OR gate 37 and connecting the outputs of ORgates32 and 37 to the input ofan AND gate 41. The X-coordinate signal isalso obtained in the same manner as above by connecting the outputs ofdiscriminators 1925 to the corresponding inputs of a digital-to-analogconverter 31. However, the Y- coordinate "signal is determined in adifferent manner as will now be described.

As shown in FIG. 3, the outputs of PM tubes 7 and 9 are connected torespective inputs-of a firstsumming network 51 and the outputs of PMtubes 11 and 13 are connected to the respective inputs of a secondsumming network 53. The outputs of summing networks 51 and 53 areconnected, respectively, to the noninverting input and the invertinginput ofan operational amplifier 55 which is wired in aconventionalmanner to provide'a signal (A) at theoutput thereof which is thedifference of the two inputs. A third summing network'57 having itsinputs connected to the outputs of the first (51) and second (53)summing networksprovides an output signal B which is the sumof allthe'signals from. the right and left ends of a strip '5. The output A ofamplifier 55 is connected to an input of a'divide'r-network 59 and theoutput B of summing network 57 is connected to the other input ofdivider 59 so that'the output of divider 59 is the Y- 'coordinatesignalequal to A divided by B. In this mode,

each PM tube may-receive only a fraction of the light signals. However,the total intensity of a-light signal can be recovered by summing allanalog signals of PM tubes on each side.

Referringnow to FIG. 4, there is shown an alternate connection schemefor agreater number of detectors such as an array of scintillationstrips '5 identical to those ofFIG. 1 and designed as (1,1), (1,2),(13), etc., through (7,7 including forty-nine strips inall. Opticallycoupledto the array of scintillation strips are a plurality of-lightconducting terminals-6l consisting of seven-P terminals ('P-l throughP-7) and seven Q terminals (Q-l through "Q-7).'These terminals aretypically made oflightconductive material and may consist of bundles oflight pipes 15 connecting the terminals 61 to the strips 5.

The strips 5 are first divided into P groups of seven strips per group.The first P group includes the strips (1,1) to (1,7), each of which isconnected by means of individual light pipes 15 to the lighttransmitting terminal P-l. The second group of strips (2,1) to (2,7)inclusive are similarly connected by individual light pipes 15 toterminal P-2 and so forth until the strips of each of the seven groupsare connected to the corresponding P terminal.

The strips 5 are then divided into Q groups with seven strips in each Qgroup as exemplified in the light pipe 15 connections to one Q terminal(0-!) as shown in FIG. 4. The first Q group connected to terminal Q-lcombines the signals from seven strips (1,1) to (7,1), inclusive. Thesecond Q group connected to terminal Q-2 combines the signals fromanother seven strips (1,2) to (7,2), inclusive and so forth until allthe terminals are similarly connected to the Q terminals 0-] throughQ-7.

When a signal is simultaneously observed in a P group and a Q group thespecific detector strip 5 activated by an event is uniquely determined.For example, if detector strip (2,1) is struck by ionizing radiation,terminal P-2 and terminal Q-l would each receive a signalsimultaneously. These simultaneous signals may be observed by two offourteen sensors, one and only one in the P group and one and only onein the Q group.

However, as shown in FIG. 5 and 6, the number of sensors, in this casephotomultiplier tubes schematically illustrated by circles 63 indicatingtheir field of view, is reduced to six for reading out the fourteen (Pand Q) terminals, shown in FIG. 4. As shown in FIG.

terminal designations P-l through P-7. The Q terminals (Q-l-throughQ'-7) are oriented in the same manner, as shown in FIG. 6.

The three. photomultiplier-tubes (PMI, PM2, and PM3) are'placed at asuitable normal distance from the terminal planeso that each PM tubereceives light signals from only one of the circled areas 63.

Thus, PMl views terminals P-1, P-3, P-5, and P-7; PM2 views P-2, P-3,P-6, and P-7; and PM3 views P-4, P-5, P-6, and P-7. Hence, light signalscoming from terminal 'P-l are received by PMl only, light signals coming from terminalP-3 will only be received by PM 1 and PM2, and so forthwith all three'PM' tubes receiving light signals from P-7 only. Theseven Q terminals are treated in the same manner, as shown inFIG. 6.

Combinatiorisofthe outputs from the PM tubes from both the P and Qgroups, therefore, uniquely determine which of the forty-nine detectorstrips 5 of FIG. 4 has detected .a radiation event which generated thelight signals. It will be understood as pointed out above that detectionsystems other than scintillation type detectors may'be read out in thesame manner. For example, a multiwiretproportiohal counter may have thecollector wires connected to corresponding P and Q terminals asthe'light pipes are connected and throughgating circuitsmay be combinedinto three outputs for each set of terminals-( P and Q) similar to the"PMtube outputs.

The arrangement shown in FIGS. 5 and 6 can be consider'ed as a binarycoding system in which the outputs of the three PM tubes in each grouprepresent the first, second, and third digits, respectively, of a binarynumber which, in turn, represents the P and Q number of the lightoutputs. For example, if an event is detected in strip (2-3) of FIG. 4,terminals P-2 and -3 will transmit light signals which activate PM2 andPMl and PM2' which is a binary representation of 010 and 011,respectively, or 2 and 3 in the base ten system.

Thus, it will be seen that the six PM tubes could be connected as inFIGS. 1-3 to provide the digital storage of events detected by the 49strips or provide an X-Y recording, as in FIGS. 2 and 3. The three PMtubes for detection on the right end of the strips 5 (FIG. 4, Qterminals) may be connected to the units inputs of a binary codeddecimal (BCD) digital-to-analog converter to replace the D/A 31 of FIGS.2 or 3. Similarly, the PM tubes for detection on the left may beconnected to the tens inputs of the BCD digital-to-analog converter aswill be explained with reference to FIG. 7. The analog output would thencorrespond to the number 11 for strip number 1, 21 for strip 8, etc.,.the last strip would correspond to number 77, the forty-ninth strip 5of FIG. 4. The remainder of the circuit of FIGS. 2 and 3 would remainessentially the same with the OR gates 33 and 37 each having threeinputs connected to the corresponding three PM tube output lines throughpulse discriminators connected, respectively to the PM tube outputs.

A similar arrangement of eight PM tubes is sufficient for 169 detectorsutilizing thirteen adjoining areas of the PM tube views corresponding tothe intersection of four overlapping circles. Thus, it is possible toconstruct large hodoscope arrays of detectors at relatively low cost forsensors, such as the PM tubes for scintillation detectors, pulseamplifiersfor multiple wire proportional counters, etc. As pointed outabove, the readout of the hodoscope may be in binary form, which relatesdirectly to the output of each PM tube, or in analog form using adigital-to-analog converter such as shown in FIGS. 2 and 3.

This invention may be further extended to provide an improved means ofmapping gamma ray images,as in a radiation camera. Referring now to FIG.7, there is shown a two-dimensional detection system using the readouttechnique of the present invention from a solid block of scintillationmaterial 71. The block 71 is fitted with a plurality of lightcollimators 73, in this case nine on each side so as to illustrate theoperation with a simplified drawing. It will be obvious from the ensuingdiscussion that any size scintillator 71 may be employed with theappropriate number of collimators 73 which will isolate a region of thematerial from which light is transmitted to divide the scintillatorblock 71 into a plurality of resolution or sensitive areas for locatingevents. Thus, the block 71 of FIG. 7 has eighty-one resolution areascorresponding to the nine light collimators 73 attached to each side ofthe block. Each collimator 73 limits the effective active area in thescintillator 71 so that only light pulses generated in a narrow band ofscintillation material directly facing a collimator can passtherethrough. This arrangement is essentially equivalent to dividing thecontinuous scintillator 71 into strips, as in FIGS. 1-3. Light pulsesproduced at any point, as at 75, in the block 71 pass through only fourcollimators, as shown by wavy lines 77 and 78 illustrating the lightpropagation normal to the corresponding four collimators 73. This is thesame as transmitting light along two orthogonal strips.

Each collimator is constructed identical with a length (A) and width (W)where W L/n, L being the length of the sides of the block 71 and n'being the number of collimators 73 along one side of the block 71. Inorder to avoid the possibility that a light pulse generated in thescintillator block 71 could conduct through more than two adjacentcollimators 73, the number of collimators should be greater than 2 L/A.Since the width W is L/n, the length (A) of each collimator should equal2 L.

The collimators 73for the X-axis are connected to light conductingterminals P-lX through P-3X at one side of block 71 and Q-lX throughQ-3X at the opposite side by means of light pipes 79 in the same manner,as illustrated in FIG. 4. The collimators 73 for the Y- axis areconnected to light conducting terminals P-lY through P-3Y on the lowerside of block 71 and terminals Q-lY through Q-3Y at the opposite, orupper, side by means of light pipes 79 in the same manner as those forthe X-axis.

Eight photomultiplier tubes 81-95 including pulse disciminators, asillustrated in FIGS. 1-3,.are used to view the various light terminalsand produce a BCD output code which is registered by a pair of BCDdigital storage means or BCD digital-to-analog converters 97 and 99 asillustrated to produce the X-coordinate and Y-coordinate outputs,respectively.

The PM tubes 81 and 83 are positioned to view the light pulses fromterminals P-1X and P-2X, respectively, while both PM tubes 81 and 83view light pulses from terminal P-3X. The nine collimators along eachside of block 71 are divided into groups of three. The collimators alongthe X-axis in group one are connected to terminal P-lX, group two toP-2X, and group three to P-3X. The outputs of PM tubes 81 and 83 areconnected to the 2, 2' inputs, respectively, of the tens decade sealerof BCD D/A 97 and indicate which of the three groups of collimators 73along the X-axis receives a light pulse generated by an event. The Q-lXthrough Q-3X terminals are connected to the three groups of collimatorsalong the other X-axis side of block 71 so that Q-lX is connected to thefirst collimator 73 of each group, Q-2X tothe second of each group, andQ-3X to the third of each group and the PM tubes 89 and 91 arepositioned to view the light from terminals Q-lX through Q-3X in thesame manner as for the PX terminals. The outputs of PM tubes 89 and 91are connected, respectively, to the 2 and 2 inputs of the units decadesealer of BCD D/A 97 to indicate the particular one of the threecollimators73 receiving light of the group indicated by the tens decade.

The Y-axis collimators 73 are connected to terminals P-lY through P-3Yand Q-lY through Q-3Y in the same manner as described above for theX-axis and viewed by PM tubes 85, 87 at the FY terminals and by PM tubes93 and 95 at the QY terminals. The PM tubes and 87 are then connected inthe same manner to the tens decade sealer of BCD D/A 99 and the PM tubes93 and are connected to the units decade sealer of BCD D/A 99 toindicate the Y-coordinate position of an event while the BIA 97indicates the X- coordinate of the event. It will be obvious here thatany number of collimators 73 and thus any practical size scintillatorblock 71 may be used with the same connection scheme as described aboveboth in reference to FIG. 7 and FIG. 4. The coding for the system wouldbe as shown in Table III for the X-axis, the Y-axis being identical.

Due to the finite length (A) and finite width (W) of each collimator itis possible for a light pulse generated in the scintillator to betransmitted through two adjacent collimators and thus to four lightterminals on each of the two axes. For example, if any event generates alight pulse at point 101 in block 71, the light would be collimated byboth collimator positions 8 and 7 along the X-axis, counting from thetop, and both collimator positions 8 and 9 on the Y-axis, counting fromthe left. Since the codings according to Table III are P: 010, :010 andP: 011, Q: 011, respectively, their overlapping would generate a code011, Le, both PMtubes for the PX terminals and the QX terminals will betriggered, therefore, it appears as though the light pulse comes fromcollimator position 9 on both axes, which would be represented in theBCD D/A convertersas the number 33. This ambiguity can be avoided byusing a reflected Gray Code instead of BCD, i.e., by rearranging theordering in the Q groups, and reassignment of codings as shown in TableIV.

With this arrangement any light pulse transmitted through two adjacentcollimators'is located as though it comes from one of the transmittingcollimators. For example, assume that an event generates a light pulseat point 101 in the scintillator block 71, then collimators in positions8 and 7 along the X-axis would receive the light pulse and collimatorsinpositions 8 and 9 along the Y-axis would receive the light pulse. Thisevent would activate all eight PM tubes when connected as shown in FIG.7. However, by reconnecting the light pipes 79 to the 0 terminals, asshown in Table IV, and repositioning the P and Q terminals with respectto the view of the corresponding PM tubes, the outputs of the PM tubeswould indicate the following code as derived from Table IV:

Collimator Position X-Axis Collimator Position Y-Axis Position CodePosition Code 7 PX:010, QX:00I B FY2010, QY:011 8 PX:010, QX:0I1 9PY:010, QY:010 Output (8) PX:010, QXzOll Output (8) PY:010, QY:011

Thus, the output location would be position 8 on the X-axis and position8 on the Y-axis. Thus, it will be seen that any light pulse transmittedthrough two adjacent collimators is located as though it came from oneof the adjacent collimators. The Gray Code to Binary Converter may beused to convert this new coding of Table IV to standard binary codingfor application to the D/A converters 97 and 99. Additional informationon Gray Code conversion may be had by reference to US. Pat. No.2,632,058 and Scientific American, cited above.

The detector readout system of FIG. 7 and its alternative connectionscheme may be used as the detecting element in a radiation pinholecamera (not shown) for mapping gamma ray images from an object such as abody organ having a distributed radioactive substance therein. The X-Ycoordinate of the light pulses from the scintillator'block 71 may bedisplayed on an X-Y oscilloscope using the analog signals at the outputsof D/A converters 97 and 99. Because of the lens effect of the pinholecollimator the X-Y location of the light pulse corresponds to aninverted X'-Y' location of the radiation gamma emitter in the source asis well known to those skilled in the art. The distribution ofradioactive substances in the source is thus imaged in a photographicrecord of the oscilloscope display as in the Anger camera.

Although the invention has been illustrated with the use ofscintillation hodoscopes, it will be understood that the readout systemis applicable to other radiation detection hodoscopes as well;

What is claimed is:

l. A digital readout system for a spatial radiation detection mediumwhich generates a signal at a location indicative of the position of aradiation event detected by one of a plurality of radiation sensitiveareas lying within a single plane in said detection medium, comprising:

a plurality of signal terminals;

a plurality of signal transmitting means for connecting respective onesof of said radiation sensitive areas of said detecting medium torespective ones of said signal terminals according to a predeterminedbinary code;

a plurality of signal sensing means responsive to signals'from selectedones of said signal terminals for generating output signals atrespective outputs thereof indicative of the location of said eventwithin said detection medium in coded digital form by the presenceor'absence-of a signal from respective ones of said-plurality of signalsensing means; and

means for recording said digital signal.

2. The readout system as set forth in claim 1 wherein said readoutsystem is a one-dimensional readout system and wherein said spatialradiation detection medium includes an array of individual detectingelements forming individual ones of said radiation sensitive areas.

3. The readout system as set forth in claim 2 wherein said array ofdetecting elements is a plurality of scintillation strips, said stripsbeing coated with a light opaque material, and wherein said signaltransmitting means includes a plurality of light pipes connected,respectively, to at least one end of each of said scintillator stripsfor transmitting light signals from said array of scintillator strips torespective ones of said plurality of signal sensing means.

4. The readout system as set forth in claim 3 wherein said plurality ofsensing means includes a plurality of photodetectors disposed to viewsaid signal terminals herein composed of the end clusters of said lightpipes, each of said photodetectors generating an electrical output upondetection of light pulses transmitted thereto from the respective one ofsaid scintillation strips, said light pipes being optically coupled tosaid plurality of photodetectors in a coded order so that the combinedoutputs of said plurality of photodetectors generates said digital codedsignal.

5. The readout system as set forth in claim 4 wherein said means forrecording said digital coded signal includes a digital-to-analogconverter having a plurality of bit inputs connected to respectiveoutputs of said plurality of photodetectors so that the amplitude of theanalog output signal of said converter is indicative of the one of saidplurality of scintillator strips detecting said radiation event.

6. The readout system as set forth in claim 1 wherein said readoutsystem is a two-dimensional readout system wherein said spatialradiation detection medium includes an array of individual detectingelements in the form of a plurality of equal length scintillationstrips, the length of said strips forming a Y-coordinate and the widthof the combined plurality of said strips forming an X-coordinate forreferencing the position of an event within said detection medium, andfurther including means for determining the Y-coordinate position ofsaid event from the output signals of said plurality of sensing means.

7. The readout system as set forth in claim 6 wherein said pluralitysignal terminals are light conducting terminals divided into first andsecond equal groups, a first plurality of light pipes connecting eachone of selected equal groupings of said scintillation strips torespective ones of said first group of terminals, a second plurality oflight pipes connecting individual ones of each of said equal groupingsof scintillation strips to respective ones of said second group ofterminals so that the activated one of said strips detecting an event islocated by a combined digital coding of the signals from said sensingmeans.

8. The readout system as set forth in claim 7 wherein said first andsecond plurality of light pipes are of equal length and wherein saidmeans for determining the Y- coordinate position includes atime-to-amplitude converter having a start input and a stop input and anoutput, a first OR gate having a plurality of inputs connected torespective outputs of said sensing means of said first group of signalterminals, a second OR gate having a plurality of inputs connected torespective outputs of said sensing means of said second group of signalterminals, said first OR gate having an output connected to said startinput of said timeto-amplitude converter and a signal delay meansproviding a time delay of at least the propagation time of a light pulsethrough the length of said scintillator strips and connected between theoutput of said second OR gate and said stop input of saidtime-to-amplitude converter.

9. The readout system as set forth in claim 1 wherein said radiationdetection medium includes a single block of scintillation materialhaving a first plurality of light collimators connected to one edge ofsaid block, a second plurality of light collimators equal in number tosaid first plurality of light collimators connected to the opposite edgeof said block and aligned respectively with said first plurality ofcollimators so that a light signal generated in said block from thedetection of an event is transmitted through at least one of said firstplurality of collimators and at least one corresponding light collimatorof said second plurality of light collimators thereby dividing saidblock of scintillation material into said plurality of sensitive areasdefined by the area of view of each pair of said first and secondplurality of light collimators.

10. The readout system as set forth in claim 9 wherein said readoutsystem is a two-dimensional readout system and further including asecond and third equal plurality of light collimators connectedidentical to said first and second pluralities of light collimatorsalong opposite edges of said block of scintillation material orthogonalto said first and second pluralities of light collimators so that theoutputs of said plurality of sensing means connected to said first andsecond pluralities and said third and fourth pluralities of lightcollimators are indicative of an X and Y coordinate position of saidevent within said block of scintillation material.

11. The readout system as set forth in claim 10 wherein said block ofscintillation material has a square radiation receiving face and whereineach of said first, second, third and fourth pluralities of lightcollimators is of identical size and number having a width at the faceadjacent the corresponding edge of said block of scintillation materialequal to the length of said face of said block divided by the number ofcollimators along the edge and a length equal to twice the length'ofsaid face of said block.

1. A digital readout system for a spatial radiation detection mediumwhich generates a signal at a location indicative of the position of aradiation event detected by one of a plurality of radiation sensitiveareas lying within a single plane in said detection medium, comprising:a plurality of signal terminals; a plurality of signal transmittingmeans for connecting respective ones of of said radiation sensitiveareas of said detecting medium to respective ones of said signalterminals according to a predetermined binary code; a plurality ofsignal sensing means responsive to signals from selected ones of saidsignal terminals for generating output signals at respective outputsthereof indicative of the location of said event within said detectionmedium in coded digital form by the presence or absence of a signal fromrespective ones of said plurality of signal sensing means; and means forrecording said digital signal.
 2. The readout system as set forth inclaim 1 wherein said readout system is a one-dimensional readout systemand wherein said spatial radiation detection medium includes an array ofindividual detecting elements forming individual ones of said radiationsensitive areas.
 3. The readout system as set forth in claim 2 whereinsaid array of detecting elements is a plurality of scintillation strips,said strips being coated with a light opaque material, and wherein saidsignal transmitting means includes a plurality of light pipes connected,respectively, to at least one end of each of said scintillator stripsfor transmitting light signals from said array of scintillator strips torespective ones of said plurality of signal sensing means.
 4. Thereadout systeM as set forth in claim 3 wherein said plurality of sensingmeans includes a plurality of photodetectors disposed to view saidsignal terminals herein composed of the end clusters of said lightpipes, each of said photodetectors generating an electrical output upondetection of light pulses transmitted thereto from the respective one ofsaid scintillation strips, said light pipes being optically coupled tosaid plurality of photodetectors in a coded order so that the combinedoutputs of said plurality of photodetectors generates said digital codedsignal.
 5. The readout system as set forth in claim 4 wherein said meansfor recording said digital coded signal includes a digital-to-analogconverter having a plurality of bit inputs connected to respectiveoutputs of said plurality of photodetectors so that the amplitude of theanalog output signal of said converter is indicative of the one of saidplurality of scintillator strips detecting said radiation event.
 6. Thereadout system as set forth in claim 1 wherein said readout system is atwo-dimensional readout system wherein said spatial radiation detectionmedium includes an array of individual detecting elements in the form ofa plurality of equal length scintillation strips, the length of saidstrips forming a Y-coordinate and the width of the combined plurality ofsaid strips forming an X-coordinate for referencing the position of anevent within said detection medium, and further including means fordetermining the Y-coordinate position of said event from the outputsignals of said plurality of sensing means.
 7. The readout system as setforth in claim 6 wherein said plurality signal terminals are lightconducting terminals divided into first and second equal groups, a firstplurality of light pipes connecting each one of selected equal groupingsof said scintillation strips to respective ones of said first group ofterminals, a second plurality of light pipes connecting individual onesof each of said equal groupings of scintillation strips to respectiveones of said second group of terminals so that the activated one of saidstrips detecting an event is located by a combined digital coding of thesignals from said sensing means.
 8. The readout system as set forth inclaim 7 wherein said first and second plurality of light pipes are ofequal length and wherein said means for determining the Y-coordinateposition includes a time-to-amplitude converter having a start input anda stop input and an output, a first OR gate having a plurality of inputsconnected to respective outputs of said sensing means of said firstgroup of signal terminals, a second OR gate having a plurality of inputsconnected to respective outputs of said sensing means of said secondgroup of signal terminals, said first OR gate having an output connectedto said start input of said time-to-amplitude converter and a signaldelay means providing a time delay of at least the propagation time of alight pulse through the length of said scintillator strips and connectedbetween the output of said second OR gate and said stop input of saidtime-to-amplitude converter.
 9. The readout system as set forth in claim1 wherein said radiation detection medium includes a single block ofscintillation material having a first plurality of light collimatorsconnected to one edge of said block, a second plurality of lightcollimators equal in number to said first plurality of light collimatorsconnected to the opposite edge of said block and aligned respectivelywith said first plurality of collimators so that a light signalgenerated in said block from the detection of an event is transmittedthrough at least one of said first plurality of collimators and at leastone corresponding light collimator of said second plurality of lightcollimators thereby dividing said block of scintillation material intosaid plurality of sensitive areas defined by the area of view of eachpair of said first and second plurality of light collimators.
 10. Thereadout system as set forth in claim 9 wherein said readout system is atwo-dimensional readout system and further including a second and thirdequal plurality of light collimators connected identical to said firstand second pluralities of light collimators along opposite edges of saidblock of scintillation material orthogonal to said first and secondpluralities of light collimators so that the outputs of said pluralityof sensing means connected to said first and second pluralities and saidthird and fourth pluralities of light collimators are indicative of an Xand Y coordinate position of said event within said block ofscintillation material.
 11. The readout system as set forth in claim 10wherein said block of scintillation material has a square radiationreceiving face and wherein each of said first, second, third and fourthpluralities of light collimators is of identical size and number havinga width at the face adjacent the corresponding edge of said block ofscintillation material equal to the length of said face of said blockdivided by the number of collimators along the edge and a length equalto twice the length of said face of said block.